1. Field of the Invention
This invention relates to gas dynamic mixing lasers and more particularly to a flowing gas laser in which an energizing gas is formed by an exothermic thermal decomposition process.
2. Description of the Prior Art
The well known gas dynamic mixing laser principle involves the rapid adiabatic expansion of a high temperature energizing gas, typically nitrogen, through an array of supersonic nozzles, mixing the energizing gas with a relatively cool lasing gas, typically carbon dioxide, in a supersonic expansion region of the nozzle and extracting laser power from the lasing gas as it passes through an optical cavity downstream of the supersonic expansion region.
A gas dynamic mixing laser is disclosed by Bronfin et al in U.S. Pat. No. 3,571,747 on "Gas Injection Laser" filed Feb. 23, 1968 and held with the present application by a common assignee, in which an energizing gas, such as nitrogen, is heated by external means and expanded through a supersonic nozzle array to create a vibrationally excited stream of gas molecules. The stream is then mixed with a relatively cool lasing gas, such as carbon dioxide, producing a population inversion of the energy levels of the lasing gas. The gas mixture than passes through an optical resonator where laser power is extracted.
Apparatus for producing a high temperature gas such as nitrogen from the thermal decomposition of a substance such as nitrous oxide is disclosed by Lewis in U.S. Pat. No. 4,002,431 filed Dec. 19, 1975 and held with the present application by a common assignee, in which liquid nitrous oxide is converted at least partially to a gaseous state as it is passed through an injector system into a decomposition chamber. The decomposition is initiated and/or maintained by an ignitor, preferably a hydrogen-oxygen device, and the heat of decomposition sustains the reaction to produce nitrogen gas having a high temperature.
Close cycle gas dynamic laser systems as disclosed by Pinsley in U.S. Pat. No. 3,886,475 filed Feb. 21, 1973 and held with the present application by a common assignee, are characterized by the recycling of the gas mixture which passes through the optical resonator. However, the efficient closed cycle operation of a gas dynamic mixing laser requires that the lasing gas be separated from the recycled energizing gas. Meliklan et al U.S. Pat. No. 3,648,194 on "Semiclosed Cycle Gas Laser System" filed Sept. 10, 1969 and held with the present application by a common assignee discloses a system in which a lasing gas such as carbon dioxide is removed from the effluent of a flowing gas laser of the mixing type of an absorptive apparatus, such as a lithium oxide or lithium hydroxide solid absorbent bed, and the remaining gases are recycled through the laser. Fresh lasing gas is injected into the system at the supersonic nozzle array from a pressurized external source. The lasing gas is removed from the gas effluent to permit recycling of the energizing gas.
A major disadvantage of the present gas dynamic mixing lasers is the need for a separate source of energy to heat the energizing gas to an elevated temperature. Excitation of the energizing gas has been accomplished utilizing electrical energy, thermal energy from a heat exchange process, and combustion processes. However, electrical excitation reduces portability, the heat exchanger is temperature limited and inefficient, and the combustion process produces undesirable chemical compositions. Furthermore, as described above, prior art closed cycle gas dynamic mixing lasers have a second major disadvantage in that they require that the lasing gas be separated from the recycling mixture. This requires introducing gas separation apparatus into the system resulting in reduced specific power of the laser.